This invention relates generally to wireless network communications and in particular to techniques for reducing power consumption in a wireless network station.
In a wireless data communication network, a node can communicate with another node, in the same network or in another network, without being wired to that node for purposes of data communication. This is accomplished by providing the node with a wireless network station. There are at least two types of nodes in a wireless network: a host (also referred to as an end node) and a hub. When a node acts as a host, it originates a transaction with another host. When a node acts as hub, it relays transactions between hosts. A host can be embodied in a mobile computer (sometimes referred to as a laptop or notebook computer) or a portable hand-held computing device such as a personal digital assistant. In such a node, the station may be a wireless network interface controller (WNIC) that communicates, via unguided electromagnetic waves, with the hub. The hub of a wireless network also has a station, though in that case the station needs to be capable of communicating with multiple other stations of the network that wirelessly connect to it. The hub acts as a distribution center for the wireless network, relaying incoming information to a destination node and relaying outgoing information from a source node.
Network nodes communicate with each other via frames (or packets) of information. A packet is routed from its source node to its destination node, and can traverse or be relayed by multiple, intermediate nodes before arriving at its destination. To deliver a packet that has originated in one network and is directed to a destination node in another network, two types of addresses are needed: (1) an upper layer address of the destination node, which may include the address of the particular network in which the destination node resides, and (2) a lower layer address of the destination node, which may include the so-called “physical” address of the destination node in that network. This layering of a network communications protocol is done because of practical difficulties that would otherwise arise for routing packets among billions of nodes, in thousands of networks around the world, if each node were to only be identified by a unique physical address.
The hub of a wireless network “knows” the lower layer addresses of all of the nodes in its network. This allows the hub to relay an incoming packet, which bears the physical address of a destination node, to that destination node. An example of a hub is an access point. The access point also allows its end nodes, which are connected to it wirelessly, to access external networks. The connection between the access point and the external networks is typically via a high speed or broadband wired link (e.g. metal wire or optical fiber), whose bandwidth is currently much greater than that of a typical wireless local area network (WLAN).
Due to practical considerations for dealing with the complexity of a large number of interconnected nodes and WLANs, although the upper layer address of a target node may be readily available to nodes outside of its WLAN, its lower layer address is generally not. However, a protocol known as the Address Resolution Protocol (ARP) has been defined for allowing a source node to obtain the lower layer address of a target destination node. With ARP, the source node broadcasts a request that identifies an upper layer address to be resolved. After being received by an access point, the request is re-broadcast in the WLAN of the access point. In this way, all nodes, including those that are connected by a wireless network, receive the ARP request. Since a node has knowledge of both its lower and upper layer addresses, the node whose upper layer address matches that of the target address specified in the ARP request responds to the request, with its lower layer address.
Nodes that are part of a wireless network may be particularly sensitive to power consumption. For instance, mobile computers and personal digital assistants are battery powered. Accordingly, there is a continuing need to ensure that such devices do not waste battery energy.